Colloidal particles with hollow interiors play important roles in microencapsulation—a process that has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments, or chemical reagents; protection of biologically active species; and removal of pollutants. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates via calcination or chemical etching. This simple and straightforward approach works for a variety of materials that include polymers, ceramics, composites, and metals. For polymers, methods such as emulsion polymerization, phase separation, crosslinking of micelles, and self-assembly have also been demonstrated for generating hollow structures. However, diffusion through these closed shells with pores less than 10 nm in diameter is often a slow process. To solve this problem, capsules have been fabricated by organizing colloids around liquid droplets to form colloidosomes or by controlling the mixing of liquid droplets.
Hollow polymer particles with holes in their surfaces have previously been created using water-soluble polymerization inhibitors when polymerizing polystyrene microparticles from styrene drops emulsified in an aqueous phase. Additionally, the use of a sacrificial-core/polymer-shell method was used to create hollow polymer particles with holes in their surfaces by controlling the amount of crosslinker in the living radical polymerization mixture.
The fabrication of polymer particles with holes in their surfaces is still difficult using current techniques. Additionally, nanometer-scale hollow polymer particles with holes in their surfaces have not yet been fabricated. There is a need for both smaller and more easily fabricated structures of this type.